In theory, fly-fishing is a simple sport: Pick a body of water, choose a fly-fishing rod, select your “fly” (or bait), tie a secure knot, cast your line and, hopefully, land a fish on the other end.

Summer can be cruel to a devout trout fisherman. I found that out during the relentless drought of 2016. By July, flows on the Farmington River—my home water in Connecticut—were reduced to a pathetic ...